The present invention provides a method and apparatus for producing aspherical surfaces.
Aspherical surfaces are widely used, particularly in optics with respect to lens and reflective surfaces. They have hitherto often been produced by rotating a workpiece of material about a first axis and using a forming tool to produce the aspheric surface. The method is diagrammatically illustrated in FIG. 1 which shows a cross section in the X-Y plane through a workpiece 10 of material in which the surface 11 is to be formed. The forming tool 12 starts from a point 0 on the axis of rotation of the workpiece 10 and moves away from this point along a locus to produce, in combination with the rotation of the workpiece 10, the desired surface 11. The movement of the tool 12 requires a combination of linear movements in the X direction and in the Y direction and requires very sophisticated control of movement of the cutting tool 12 in the two linear directions. At all times the tool 12 must be moving in the direction of a tangent to the curve as is illustrated in FIG. 1. The direction of motion of the tool 12 at two points, P1 and P2 as the surface 11 is generated is indicated by lines T1 and T2 and the resultant motions in the X and Y direction RX1, RY1 at point P1 and RX2, RY2 at point P2 are shown.
The control of such resultant linear movements which are not constant to the very fine tolerances required by optical apparatus is very difficult. The apparatus is therefore expensive to manufacture and must be carefully operated and properly maintained if sufficient accuracy is to be achieved.